A known method for assembling a cylinder block, a cylinder head, and a chain cover of an engine will be explained below.
The cylinder head is assembled on the cylinder block while a solid gasket (a plate-shaped gasket) serving as a first seal member is disposed or sandwiched between an upper joint surface of the cylinder block and a lower joint surface of the cylinder head. As a result, a clearance between the cylinder block and the cylinder head is closed.
Then, a liquid gasket (a liquid sealing agent) serving as a second seal member is applied to a lateral joint surface of the chain cover to thereby assemble the chain cover on the cylinder block and the cylinder head that are assembled on each other.
At this time, the liquid gasket applied to the lateral joint surface of the chain cover makes contact with a lateral joint surface of the cylinder block and a lateral joint surface of the cylinder head so as to close a clearance among the chain cover, the cylinder block, and the cylinder head. Accordingly, the cylinder block, the cylinder head, and the chain cover are assembled on each other while a sealing ability is secured.
At a time of an engine operation, however, wall portions of the cylinder block and the cylinder head are exposed to a combustion gas having a high temperature. Specifically, the cylinder head tends to be more heated than the cylinder block and thus tends to expand due to heat (i.e., a thermal expansion). Therefore, a relative displacement between the cylinder head and the cylinder block in a longitudinal direction of the engine may be generated, which leads to a clearance between the lateral joint surface of the chain cover and the lateral joint surface of the cylinder block at a joint portion among the cylinder block, the cylinder head, and the chain cover. At this time, the liquid gasket filled in the clearance among the cylinder block, the cylinder head, and the chain cover is affected by an excessive tensile deformation, which may lead to a deterioration of the sealing ability of the liquid gasket.
Further, at the time of the engine operation, depending on a material of the cylinder head or the cylinder block, a shape of the solid gasket, and the like, the degree of the thermal expansion of the cylinder head and that of the cylinder block may vary. Therefore, an end surface of the chain cover facing the lateral joint surface of the cylinder head and/or the lateral joint surface of the cylinder block is positioned away therefrom. Then, a clearance may be formed between the lower joint surface of the cylinder head and the upper joint surface of the cylinder block at the joint portion among the cylinder block, the cylinder head, and the chain cover. At this time, the liquid gasket with which the clearance is filled is affected by the excessive tensile deformation, which may lead to the deterioration of the sealing ability of the liquid gasket.
In order to solve the aforementioned issue, JP2005-188375A discloses a seal structure for an engine including a cut portion serving as a holding recess portion at which the liquid gasket is retained so that the cut portion is filled therewith. The cut portion is formed at a corner on an outer surface of the cylinder block at the joint portion among the cylinder block, the cylinder head, and the chain cover.
According to the seal structure disclosed in JP2005-188375A, the cylinder head is assembled on the cylinder block while the solid gasket is disposed or sandwiched between the upper joint surface of the cylinder bock and the lower joint surface of the cylinder head. Then, the liquid gasket, of which an amount is slightly greater than a required amount for closing the clearance among the cylinder block, the cylinder head, and the chain cover, is applied to the lateral joint surface of the chain cover. The chain cover is then assembled on the cylinder block and the cylinder head, which are assembled on each other.
At this time, the liquid gasket applied to the lateral joint surface of the chain cover makes contact with the lateral joint surface of the cylinder block and the lateral joint surface of the cylinder head to thereby close the clearance among the cylinder block, the cylinder head, and the chain cover. At the same time, the excess liquid gasket from the clearance among the cylinder block, the cylinder head, and the chain cover is pushed to the cut portion formed at the cylinder block.
When the engine is in operation, even in a case where the clearance is generated between the lateral joint surface of the chain cover and the lateral joint surface of the cylinder block or between the lower joint surface of the cylinder head and the upper joint surface of the cylinder block, the liquid gasket, with which the cut portion is filled, flows to be filled in such clearance. Therefore, the sealing ability of the liquid gasket is maintained.
However, the assembly of the chain cover on the cylinder bock and the cylinder head that are assembled on each other after the application of the liquid gasket only to the lateral joint surface of the chain cover may not achieve a secure filling of the liquid gasket at the cut portion.
In addition, because the cut portion is formed at the outer surface of the cylinder block, it may be difficult to determine whether the cut portion is practically sufficiently filled with the liquid gasket.
A need thus exists for a seal structure for an engine which is not susceptible to the drawback mentioned above.